Method for seamless coating of printing forms



Oct. 1, 1957 R. KAULEN ET AL 2,508,344

METHOD FORSEAMLESS COATING OF PRINTING FORMS Filed May 28, 1954 lNl/ENTORC W Krohe AP R. Kclulerp By a ATTYS.

United States Patent This invention relates to a method of and a device for seamless coating of printing forms, especially of printing cylinders or copper cylinders, with a photo-colloidsolution which is a layer sensitive to light.

Several methods are already known for providing copper cylinders with a seamless layer of photo-colloid. For instance, the layer has been applied upon a cylinder disposed within a horizontal centrifugal machine and rotat ing about its own axis. Further, it has heretofore been attempted to form the layer upon the cylinder rotating in a lathe by applying the overflowing colloid by means of a slide rest'or the like. There is also known the use of a ring through which the cylinder is drawn. With the hitherto known methods a uniform thickness of the layer cannot be obtained. Besides, the result of the coating process depends largely on the ability of the operating person and a reliable operation cannot be assured. In printing cylinders which have to be used for endless printing of long sheets as, for instance, sheets of paper, it is necessary especially in multicolor printing that the layer is always even and uniform as otherwise displacements of the patterns in endless printing result.

The present invention has for its object a method and a device which provides a completely uniform coating in a simple and reliable manner. The method according vto the invention is essentially characterized in that the colloid solution in the container receiving the printing form is kept at a constant level and that the printing form is drawn up within the container in its longitudinal direction and is subjected at the free end thereof to the influence of heat. Preferably, the colloid solution is discharged from the container at the height of the solution level during drawing up the printing form from the container. Suitably, the layer applied to the printing form is progressively dried upon leaving the colloid solution. Further, it is of importance that wetting of the printing form by the colloid solution is eflected in such a manner that the solution introduced into the container receiving the printing form is rising from the bottom of the container. The method according to the present invention offers the advantage that a completely even layer of uniform thickness is obtained. Troubles and damages by the formation of bubbles are prevented. The method assures a secure and clean operation.

The device for carrying out the method according to the invention is preferably formed in such a manner that the container is provided with a piston-like bottom which is moved simultaneously with the printing form drawn up from within the container. The container is provided with an overflow for keeping constant the level of the colloid solution, The printing form is guided on the one hand by the bottom of the container which is moved simultaneously with the printing form and on the other hand by an upper support. Preferably, the printing form may be drawn up from the container with adjustable speed. The variation of the speed influences the thickness of the applied layer. The supply of the colloid solution is suitably efi'ected through the movable bottom 2,808,344 Patented Oct. 1, 1957 so that the colloid solution may rise into the container. Filling of the container with the solution is eflected in this manner by a laminar current. The formation of bubbles is thereby; prevented. Such a device assures a ice reliablea-nd uniform result of the operation. Cleansing of the device is very simple.

The figure on theQdrawi-ng illustrates by way of example one embodiment of the device according to the invention. I

The container 1 which receives the colloid solution and the printing form to be coated, preferably the printing cylinder, is advantageously formed as a tube. It may be provided with a jacket 2 to keep the colloid solution within the tube 1 at a fixed temperature. The printing cylinder 3 is mounted in such a manner in the container l'that it is movable in a longitudinal direciton. The bottom 4 of the container is movable in tube 1 and it is suitably formed as a piston which closely seals tube 1 by means of the packing ring 5. For keeping constant the level of the colloid solution, the container 1 is provided with an overflow 6 which is formed as an annular channel with a continuous slot or with single openings.

T he axle 3a of printing cylinder 3 is fixed thereto and is journaled in guide bearing 7. The bearing is formed in such a manner that it may be moved in the direction of the longitudinal axis of the printing cylinder by means of a mechanical or an electrical drive. In the extension of the axis of container 1 a heating device is suitably provided by means of which the applied colloid layer may be dried.

The colloid solution is suitably supplied to the container 1 through bottom 4. The excess of the solution is taken by a storage container 10 from overflow pipe 6 into which is inserted a filtering device 13. Supply pipe 9 opens into storage container 10 which is suitably arranged laterally from container 1.

The coating process according to the invention is effected as follows:

After insertion of the printing cylinder 3 into container 1, the colloid solution is introduced from storage container 10 from below into container 1, for instance, by means of compressed air which is supplied to the closed storage container by means of pipe 11. The excess of the colloid solution returns into container 10 through overflow pipe 6. Now valve 12 of supply pipe 9 is closed. After that, cylinder 3 is drawn up slowly from tube 1, for instance, by means of a gear, the piston-like bottom 4 being moved simultaneously therewith. Pipe 9 may be interrupted beneath valve 12 or may consist of a sufficiently long flexible tube. The displaced colloid solution is discharged through overflow pipe 6. The speed of the upward movement depends on the desired thickness of the layer. The heating device 8, preferably an electrical heating device, provides for rapid drying of the appliedlayer immediately upon the same leaving the colloid solution.

Whatis claimed as new, is:

1. A method for seamless coating of printing forms, particularly printing cylinders with a colloid solution which comprises the following successive steps; mounting a printing form in an emptycontainer, supplying a colloid solution intothe container from below the printing form to a level in the container above the printing form, raising the printing form from within the container and causing the lower level of the solution to move therewith while discharging the solution at the upper level thereof and maintaining the upper level thereof constant and the solution substantially static between said upper and lower levels, and subjecting the printing form to the influence of heat upon leaving the solution.

2. The method of claim 1 wherein said influence 0f solution whichcomprises mounting the elongated form vertically Within a surrounding and closely conforming but spaced zone, introducing the colloidal solution into said zone, then raising simultaneously the form and the bottom of the zone, retaining the upper level of the colloidal solution constant during the raising of the form solely by overflow of said colloidal solution, and harden ing the film on the form by heating as the form emerges from the solution.

UNITED STATES PATENTS Hubbell May 23, Powell Jan. 1, McCullough Oct. 22, Linder May 2, Beaune June 9, Green Nov. 3, Lippincott Sept. 12, Kooh Aug. 25, Spencer Jan. 20, 

1.A METHOD FOR SEAMLESS COATING OF PRINTING FORMS, PARTICULARLY PRINTING CYLINDERS WITH A COLLOID SOLUTION WHICH COMPRISES THE FOLLOWING SUCCCESSIVE STEPS; MOUNTING A PRINTING FORM IN AN EMPTY CONTAINER, SUPPLYING A COLLOID SOLUTION INTO THE CONTAINERFROM BELOW THE PRINTING FORM TO A LEVEL IN THE CONTAINER ABOVE THE PRINTING FORM, RASING THE PRINTING FORM FROM WITHIN THE CONTAINER AND CAUSING THE LOWER LEVEL OF THE SOLUTION TO MOVE THEREWITH WHILE DISCHARGING THE SOLUTION AT THE UPPER LEVEL THEREOF AND MAINTAINING THE UPER LEVEL THEREOF CONSTANT AND THE SOLUTION SUBSTANTIALLY STATIC BETWEEN SAID UPPER AND LOWER LEVELS, AND SUBJECTING THE PRINTING FORM TO THE INFLUENCE OF HEAT UPON LEAVING THE SOLUTION. 